Extreme pain while using spirometer.

My father just had bypass surgery a little while ago and is having to use a spirometer several times a day. Today while visiting him he asked me to try the spirometer and see how high I could get the ball to go. I did it the first time, tried a second time, and the third time I breathed out all of the air in my lungs and then proceeded to breathe in from the tube slowly. When I got towards the end of my lung capacity, all of the sudden I had extreme sharp pain on my back (it felt like someone had punched me in both of my kidneys) that quickly traveled up each side of my back. The left side stopped midway up but the right side traveled up into the right side of my neck. I've never felt any pain like this before from breathing, but I am a smoker. Any ideas what that was all about? The pain lasted for about 1 minute intensely, and then gradually receded over the next 5 minutes.